LIDAR sensors are used, for example, in driver assistance systems for motor vehicles for detecting the traffic environment, for example locating preceding vehicles and other obstacles.
The electrooptical (optoelectronic) elements of the detector surface are situated in a row or in a plane, and are sensitive to light that has been received from a specific direction for the particular element, so that a one-dimensional or two-dimensional image is obtained. By measuring the propagation times of the light pulses, the distances from the reflecting objects may also be determined, so that a depth-resolved two-dimensional or three-dimensional image of the surroundings is obtained.
However, the measured signal propagation times are a function not only of the distances from the objects, but also of the properties of the evaluation circuit, since relaying the electronic signals in the evaluation circuit also requires a certain amount of time, so that the detection times ultimately measured are delayed by the propagation time of the electronic signals in the evaluation circuit. During the manufacture of the LIDAR sensors, at the end of the production line it is therefore customary to carry out a calibration in which the propagation time of the electronic signals is determined.
However, the propagation times of the electronic signals in the evaluation circuit may change over time due to temperature changes or aging effects. In one conventional method, these effects are detected and compensated for by decoupling light pulses directly at the light source, using a beam splitter, and deflecting them onto a reference surface which, the same as the detector surface, is equipped with optoelectronic elements for receiving the decoupled light. The detection times for the decoupled light pulses on the reference surface may then be used as a time reference, but only under the condition that there is a high level of symmetry between the detector surface and the reference surface as well as the associated electronic connections to the evaluation circuit, so that the propagation times of the electronic signals from the detector surface and the reference surface sufficiently match.